add code tabs in num12.

_overviews/scala3-book/taste-objects.md

@@ -19,27 +19,43 @@ Objects have several uses:
   In this situation, that class is also called a _companion class_.
 - They’re used to implement traits to create _modules_.
 
-
-
 ## “Utility” methods
 
 Because an `object` is a Singleton, its methods can be accessed like `static` methods in a Java class.
 For example, this `StringUtils` object contains a small collection of string-related methods:
 
+
+{% tabs object_1 class=tabs-scala-version %}
+{% tab 'Scala 2' for=object_1 %}
+```scala
+object StringUtils {
+  def isNullOrEmpty(s: String): Boolean = s == null || s.trim.isEmpty
+  def leftTrim(s: String): String = s.replaceAll("^\\s+", "")
+  def rightTrim(s: String): String = s.replaceAll("\\s+$", "")
+}
+```
+{% endtab %}
+
+{% tab 'Scala 3' for=object_1 %}
 ```scala
 object StringUtils:
   def isNullOrEmpty(s: String): Boolean = s == null || s.trim.isEmpty
   def leftTrim(s: String): String = s.replaceAll("^\\s+", "")
   def rightTrim(s: String): String = s.replaceAll("\\s+$", "")
 ```
+{% endtab %}
+{% endtabs %}
 
 Because `StringUtils` is a singleton, its methods can be called directly on the object:
 
+{% tabs object_2 %}
+{% tab 'Scala 2 and 3' for=object_2 %}
 ```scala
 val x = StringUtils.isNullOrEmpty("")    // true
 val x = StringUtils.isNullOrEmpty("a")   // false
 ```
-
+{% endtab %}
+{% endtabs %}
 
 ## Companion objects
 
@@ -48,6 +64,27 @@ Use a companion object for methods and values which aren’t specific to instanc
 
 This example demonstrates how the `area` method in the companion class can access the private `calculateArea` method in its companion object:
 
+{% tabs object_3 class=tabs-scala-version %}
+{% tab 'Scala 2' for=object_3 %}
+```scala
+import scala.math._
+
+class Circle(radius: Double) {
+  import Circle._
+  def area: Double = calculateArea(radius)
+}
+
+object Circle {
+  private def calculateArea(radius: Double): Double =
+    Pi * pow(radius, 2.0)
+}
+
+val circle1 = new Circle(5.0)
+circle1.area   // Double = 78.53981633974483
+```
+{% endtab %}
+
+{% tab 'Scala 3' for=object_3 %}
 ```scala
 import scala.math.*
 
@@ -62,13 +99,36 @@ object Circle:
 val circle1 = Circle(5.0)
 circle1.area   // Double = 78.53981633974483
 ```
-
+{% endtab %}
+{% endtabs %}
 
 ## Creating modules from traits
 
 Objects can also be used to implement traits to create modules.
 This technique takes two traits and combines them to create a concrete `object`:
 
+{% tabs object_4 class=tabs-scala-version %}
+{% tab 'Scala 2' for=object_4 %}
+```scala
+trait AddService {
+  def add(a: Int, b: Int) = a + b
+}
+
+trait MultiplyService {
+  def multiply(a: Int, b: Int) = a * b
+}
+
+// implement those traits as a concrete object
+object MathService extends AddService with MultiplyService
+
+// use the object
+import MathService._
+println(add(1,1))        // 2
+println(multiply(2,2))   // 4
+```
+{% endtab %}
+
+{% tab 'Scala 3' for=object_4 %}
 ```scala
 trait AddService:
   def add(a: Int, b: Int) = a + b
@@ -84,12 +144,12 @@ import MathService.*
 println(add(1,1))        // 2
 println(multiply(2,2))   // 4
 ```
+{% endtab %}
+{% endtabs %}
 
 {% comment %}
 NOTE: I don’t know if this is worth keeping, but I’m leaving it here as a comment for now.
 
 > You may read that objects are used to _reify_ traits into modules.
 > _Reify_ means, “to take an abstract concept and turn it into something concrete.” This is what happens in these examples, but “implement” is a more familiar word for most people than “reify.”
 {% endcomment %}
-
-